1. Field of the Invention
The present invention relates in general to making up and breaking out pipe connections during drilling operations and, in particular, to a tool for allowing circulation of fluid through and rotation of a pipe string while making up or breaking out pipe connections.
2. Brief Description of Related Art
In conventional drilling operations, well bores are drilled with a drill bit on the end of a pipe string that is rotated by means of a rotary table or a top drive. The top drive is coupled to the upper end of the pipe string and provides the necessary torque to rotate the drill bit for continued drilling. Typically, a pump circulates drilling mud through the top drive and down the pipe string to the drill bit during drilling operations. Continued pumping through the top drive forces the drilling mud at the bottom of the wellbore back up the wellbore on the outside of the pipe string, where the drilling mud returns to a drilling mud tank system. The circulating drilling mud cools and cleans the drill bit, bringing the debris and cuttings produced by the drilling process to the surface of the wellbore. Continued drilling draws the pipe string further into the wellbore, eventually requiring another stand of pipe to be added to the pipe string.
In most prior art drilling methods, when a new stand is added to or removed from the pipe string, rotation of the pipe string, and thus drilling, must cease for the duration of the period needed to complete the new joint make up. Prolonged periods without rotation causes prolonged static contact between the formation surrounding the pipe string and the pipe string. This static contact increases the risk of the pipe string becoming stuck in the wellbore. A stuck pipe string causes significant problems for the drilling operation that must be overcome at great expense of time and money. Therefore, there is a need for a device that allows for continuous or nearly continuous rotation of the pipe string while making up or breaking out a new stand.
Circulation of the drilling mud through the pipe string must also cease for the duration of the period needed to add a stand to or remove a stand from the pipe string. When circulation of drilling mud stops, the pressure on the wellbore can significantly decrease. This can cause sections of the wellbore to cave in, or allow the higher pressure of the surrounding formation to cause a blowout of the well. Particularly in a blowout event, this can cause significant risk to property and life. In addition, the cuttings or other debris produced by the drilling process that are carried up and out of the wellbore by the drilling mud may settle when circulation stops, binding the drill bit or causing the pipe string to become stuck. Again, a bound drill bit or stuck pipe string can cause significant problems for the drilling operation that must be overcome at great expense of time and money. Therefore, there is a need for a device that provides continuous or nearly continuous circulation of drilling mud through the pipe string during stand make up or break out.
Various attempts to overcome the problems associated with pipe string make up and break out have been tried. For example, some prior art devices couple a cylinder type device around the pipe string and stand to be joined. The devices employ various sealing elements to alternately close off the pipe string or the stand during make up or break out. Drilling mud circulates into the pipe string through a connection at the cylinder while the stand is being made up or broken out, allowing for continuous circulation. Typically, the devices are quite complex and, to properly operate the device, necessitate the addition of costly and space consuming equipment to the drilling rig. In addition, while these devices continue circulation of the drilling mud, they cannot maintain rotation of the pipe string while a new stand is made up or broken out. Their inability to maintain rotation continues to cause stuck pipe string problems.
Other attempts to overcome these problems couple an element inline with the pipe string at every new stand; the element providing an alternate drilling mud circulation path. These elements provide a coupling for a drilling mud circulation device to attach to during stand make up or break out. The elements typically contain a valve at an upper end of the element that directs drilling mud flow down the pipe string and not back up the new stand when drilling mud circulates along the alternate circulation path. In this manner, these inline elements achieve continuous circulation through the pipe string. However, as above, the inline elements do not provide a solution to achieve continuous rotation. Therefore, there is a need for a device that can maintain continuous circulation and rotation during make up or break out of a stand.